PARIS: By 2050, more than half the global population will live downstream from tens of thousands of large dams near or past their intended lifespan, according to a UN report released Friday.

Most of the world’s nearly 59,000 big dams — constructed between 1930 and 1970 — were designed to last 50 to 100 years, according to research from the UN University’s Institute for Water, Environment and Health.

Dozens have suffered major damage or outright collapse over the last two decades in the United States, India, Brazil, Afghanistan and other countries, and the number of such failures could increase, the report warned.

A global fleet of nearly 60,000 ageing dams also highlights the challenge of dismantling — or “decommissioning” — those that are no longer safe or functional.